Generally, polymers are superior to other materials in processability, mechanical strength, electrical insulation, optical transparency and mass production, and are being used as an important new material in the field of high-tech industry such as semiconductor, electrical and electronic industry, aerospace, defense industry, display and alternative energy. As a dielectric material, polymer materials have advantages because they can obtain various properties by molecular design and are very well suited for molding, while they have poor dielectric properties and lower thermal or mechanical properties than inorganic materials, significantly limiting the applications as a new material.
Currently, attempts are being made to study the dielectric properties of polymers for the purpose of use as high-k gate dielectrics for flexible electronic materials, dielectric elastomer actuators (DEAs) and touch sensors.
Particularly, touch panel technology can be used in a variety of electronic/communication devices such as laptop computers, personal digital assistant (PDA), game consoles, smart phones and navigation, and can be used to select or input functions desired by users. Such touch panel technology is largely implemented by resistive approach and capacitive approach. Capacitive touch sensors not only allow for multi-touch but also can sense contact position and contact force. Dielectric materials necessary for these touch sensors need not only high permittivity of 10 or more but also a low modulus of elasticity and a high adhesive strength with electrode to increase the capacitance. First of all, to fabricate reliable sensors, it is necessary to ensure high reliability of dielectric materials.
Polymer materials having a high dielectric constant are an ideal material for a wide range of electronic material applications because they are free from problems caused by dispersion in multiphase systems when they form a single phase. Recently, Pennsylvania State University research team reported a method for preparing PVDF electroactive copolymers having a dielectric constant of 100 by a method which treats a PVDF copolymer film by radiation, following by poling with an electric field, Shizuoka University in Japan developed materials having a dielectric constant of 20 or more using polymer having a polar cyano group, German Plastic Institute and University of Wales in U.K. prepared polymer dielectrics having a dielectric constant of 8 or more using PVDF and its related copolymers. However, these materials have a limitation on the applications of capacitive touch sensors due to a high price, a low yield and a high modulus of elasticity.
To solve the problem, studies have been made to form a composite of high-k filler and elastomer to increase the dielectric constant of the elastomer. Japanese Patent Publication No. 2008-239929 and Japanese Patent Publication No. 2005-177003 added a ceramic filler including lithium to thermoplastic elastomer to increase the dielectric constant at a low cost, WO98/04045 discloses electroactive polymer using a composite in which a conductive filler such as carbon black, graphite and metal particles is added to elastomer, and besides, research is being conducted by many groups to ensure a high dielectric constant of elastomer by dispersing a conductive filler having a large aspect ratio of one dimension such as carbon nanotubes in elastomer.
However, these insulator/conductor composites are only focused on improved dielectric properties, and they were found unsuitable for high dielectric properties, an adhesive strength with electrode, a low modulus of elasticity and a high reaction speed required for force sensors.